1. Field of the Invention
The present invention relates to a pressure and flow control apparatus, and a plant system using the same. More particularly, the present invention relates to a pressure and flow control apparatus in which a pressure control valve is connected with another control valve in series.
2. Description of the Related Art
To control a pressure and a physical quantity of fluid at the same time, a pressure control valve and anther control valve are connected in series.
FIG. 1 shows a conventional pressure and flow control apparatus. Referring to FIG. 1, the conventional pressure and flow control apparatus is composed of a pressure control valve 101 and a flow rate control valve 102. A pipe 103 is connected with the input side of the pressure control valve 101. A pipe 104 is connected between the output side of the pressure control valve 101 and the input side of the flow rate control valve 102. The output side of the flow rate control valve 102 is connected with a pipe 105. The fluid is introduced into the pipe 103, and is led to the pipe 104 through the pressure control valve 101. Then, the fluid in the pipe 104 is led to the pipe 105 through the flow rate control valve 102.
The opening degree of the pressure control valve 101 is controlled by a pressure gauge 106, a difference unit 107 and a pressure control unit 108. The pressure gauge 106 measures the pressure XP in the pipe 104. The difference unit 107 calculates the difference between the measured pressure XP and a reference pressure RP to obtain a deviation EP. The degree UP of the pressure control valve 101 based on the deviation EP. The opening degree of the pressure control valve 101 is set to the determined opening degree UP. As a result, the pressure XP of the pipe 104 is controlled to be coincident with the reference pressure RP.
Also, the opening degree of the flow control valve 102 is controlled by a flowmeter Fx 109, a difference unit 111, and a flow control unit 112. The flowmeter FX 109 measures the flow rate XF of the fluid flowing through the pipe 105. The difference unit 111 calculates a difference between the measured flow rate XF and a reference flow rate RF to obtain a deviation EF. The flow control unit 112 determines the opening degree UF of the flow control valve 102 based on the deviation EF. The opening degree of the flow control valve 102 is set to the determined opening degree UF. As a result, the flow rate XF of the fluid flowing through the pipe 105 is controlled to be coincident with the reference flow rate RF.
In the above-mentioned pressure and flow control apparatus, the opening degree of the flow control valve 102 has an influence on the pressure XP of the pipe 104 which depends on the opening degree of the pressure control valve 101. Therefore, it is desirable that the pressure XP of the pipe 104 is controlled, considering such an influence.
Especially, when the opening degree of the flow control valve 102 is small, the pressure control valve 101 often repeats a switching operation between a small opened state and a full closed state. The repetition causes the damage and abrasion of a valve sheet of the pressure control valve 101. Therefore, it is desirable that the repetition of the switching operation is not carried out in the pressure control valve 101, even if the opening degree of the flow control valve 102 is small.
In conjunction with the above description, a fuel flow rate control apparatus for a turbine is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 7-54672). In this reference, a fuel-adjusting pipe is connected to a fuel supply system and has a closed portion at one end and a fuel-blowing hole on a side portion. A casing is provided around the fuel-adjusting pipe and connected with a fuel consuming system. A flap valve is provided near the fuel-blowing hole to be movable in a longitudinal direction of the fuel-adjusting pipe for setting an opening quantity of the fuel-blowing hole. A position sensor detects the position of the flap valve. A torque motor is connected to the position sensor and the flap valve and drives the flap valve based on a fuel instruction value and position detection data by the position sensor.
Therefore, an object of the present invention is to provide a pressure and flow control apparatus in which a pressure control valve is connected to another control valve in series, and the opening degree of the pressure control valve is controlled considering the opening degree of the other control valve.
Another object of the present invention is to provide a pressure and flow control apparatus in which a pressure control valve is connected to another control valve in series, and the pressure control valve does not repeat a switching operation between a small open state and a full close state even if the opening degree of the other control valve is small.
Still another object of the present invention is to provide a pressure and flow control apparatus in which a pressure control valve is connected to another control valve in series, and a damage and abrasion of a valve sheet of the pressure control valve can be prevented.
Yet still another object of the present invention is to provide a plant system having any of the above pressure and flow control apparatuses.
In an aspect of the present, a pressure and flow control apparatus includes first to third pipes, fluid being supplied to the first pipe and outputted from the third pipe, a pressure control valve, a control valve, and a control unit. The pressure control valve is provided between the first and second pipes and opened or closed based on a first opening degree to control flow of the fluid from the second pipe to the third pipe. The control valve is provided between the second and third pipes and opened or closed based on a second opening degree to control flow of the fluid from the first pipe to the second pipe. The control unit determines the first opening degree, and determines the second opening degree based on the first opening degree and a pressure in the second pipe.
Here, the control unit preferably determines the first opening degree based on a physical parameter. In this case, the control unit may include a detecting unit provided for the third pipe to detect the physical parameter. Otherwise, the control unit may include a detecting unit provided for an output of a unit which operates using the fluid outputted from the third pipe, to detect the physical parameter. The physical parameter is one of temperature and flow rate.
Also, the control unit may determine the first opening degree based on the physical parameter and a first reference value.
Also, the control unit may include a pressure-detecting unit which detects the pressure in the second pipe.
Also, the control unit may determine the second opening degree such that the second pressure control valve is always opened as far as the control valve is opened.
In another aspect of the present invention, a pressure and flow control apparatus includes first to third pipes, fluid being supplied to the first pipe and outputted from the third pipe, a pressure control valve, a control valve and a control unit. The pressure control valve is provided between the first and second pipes and opened or closed based on a first opening degree to control flow of the fluid from the second pipe to the third pipe. The control valve is provided between the second and third pipes and opened or closed based on a second opening degree to control flow of the fluid from the first pipe to the second pipe. The control unit determines the first opening degree, determines a first temporary opening degree based on the first opening degree, determines a second temporary opening degree based on a pressure in the second pipe, and determines the second opening degree based on the first and second temporary opening degrees.
Here, the control unit may include a function unit which outputs the first temporary opening degree based on the first opening degree. In this case, the function unit may output the first temporary opening degree of a value depending on the first opening degree in a first range of the first opening degree. It is preferable that the value depending on the first opening degree monotonously increases depending on increase of the first opening degree. Also, the function unit may output the first temporary opening degree of a constant value in a second range of the first opening degree between 0 and the first range of the first opening degree.
Also, the control unit may include a selector which selects one of the first and second temporary opening degrees as the second opening degree.
Also, the control unit may include a pressure-calculating unit which determines the second temporary opening degree based on the pressure in the second pipe and a reference pressure.
Also, the control unit may include a detecting unit which detects a physical parameter which is influenced by the control valve, and a calculating unit which determines the first opening degree based on the detected physical parameter and a reference value.
In still another aspect of the present invention, a gas turbine system includes a gas turbine which operates using a fuel gas, and a pressure and flow control apparatus. The pressure and flow control apparatus has a pressure control valve and a flow rate control valve which are connected in series. The pressure and flow control apparatus controls a first opening degree of the flow rate control valve to control a flow rate of the fuel gas supplied to the gas turbine, and controls a second opening degree of the pressure control valve based on a pressure of the fuel gas on an output side of the pressure control valve and the first opening degree such that the pressure of the fuel gas supplied to the gas turbine is controlled.
Here, the control unit may determine the first opening degree of the flow rate control valve based on the flow rate of the fuel gas supplied to the gas turbine. Also, the control unit may determine a first temporary opening degree based on the first opening degree, determine a second temporary opening degree based on the pressure on the output side of the pressure control valve, and determine the second opening degree based on the first and second temporary opening degrees.
Also, the control unit may determine the second opening degree such that the second pressure control valve is always opened as far as the control valve is opened.
Also, the control unit may include a selector which selects one of the first and second temporary opening degrees as the second opening degree.
In yet still another aspect of the present invention, a steam turbine system includes a steam turbine, a bypass section, a boiler, and a pressure and flow control apparatus. The steam turbine includes a first turbine operating using a main steam and then outputting low temperature re-heated steam, and a second turbine operating high temperature re-heated steam. The bypass section has a cooler using water to cool a part of the main steam and to produce the low temperature re-heated steam. The boiler generates the main steam to supply to the steam turbine and heats the low temperature re-heated steam from the steam turbine and the bypass section to produce and supply the high temperature re-heated steam to the steam turbine. The pressure and flow control apparatus has a pressure control valve and a temperature control valve which are connected in series. The control apparatus controls a first opening degree of the temperature control valve based on a temperature of an output of the cooler such that supply of the water to the cooler is controlled, and controls a second opening degree of the pressure control valve based on a pressure on an output side of the pressure control valve and the first opening degree such that the pressure of the water supplied to the cooler is controlled.
Also, the control unit may determine the first opening degree of the flow rate control valve based on the temperature of the output of the cooler, determine a first temporary opening degree based on the first opening degree, determine a second temporary opening degree based on the pressure on the output side of the pressure control valve, and determine the second opening degree based on the first and second temporary opening degrees.
Also, the control unit may determine the second opening degree such that the second pressure control valve is always opened as far as the temperature control valve is opened.
Also, a selector selects one of the first and second temporary opening degrees as the second opening degree.